1. Field of the Invention
The present invention relates to semiconductor devices and, more particularly, to a semiconductor device in which a semiconductor element is mounted on a substrate by wire-bonding.
2. Description of the Related Art
In recent years, high-densification of semiconductor element has progressed, which causes a reduction in a pitch of electrode terminals formed on an semiconductor element. Additionally, a processing speed of input and output signals has been increased, which results in, in many cases, provision of electrode terminals for inputting and outputting high-frequency signals.
High-frequency signal lines connected to the electrode terminals for outputting and inputting high frequency signals need to take impedance-matching with peripheral circuits and wirings. Generally, a differential pair is formed by two high-frequency lines, and the differential pair is located between shielding lines such as a grounding line, a power supply line, etc.
Generally, in a semiconductor device, electrodes of a semiconductor element are arranged along a periphery (each side) of the semiconductor element, and the semiconductor element is mounted on a substrate and electrically connected to the substrate by bonding wires. The thus-constructed semiconductor device can be manufactured using a previously-established technology, and, thus, can be manufactured at a relatively low-cost.
For example, Japanese Laid-Open Patent Application No. 6-6151 discloses a semiconductor device having the above-mentioned structure.
If a high-densification technique like a semiconductor element fabricating-technique is used for manufacturing a substrate on which a semiconductor element is mounted, a manufacturing cost of the substrate is increased. For this reason, generally, a substrate is manufactured using a technique to manufacture a low-density structure as compared to that of a semiconductor element. Such a substrate is referred to as a low-cost substrate.
It is difficult to form high-density wiring on the low-cost substrate, which increases an area (size) of a substrate. However, since the cost of a semiconductor device can be reduced by using the low-cost substrate, the low-cost substrate is used widely. With high-densification of semiconductor elements, a pitch of electrodes of semiconductor elements has become much smaller than a pitch of terminals of the low-cost substrate.
Therefore, in a case where electrodes arranged in a peripheral part of a semiconductor element are wire-bonded to terminals of a substrate, the wire-bonding is performed on the terminals of the substrate while gradually increasing an interval of the adjacent bonding-wires.
Additionally, the terminals of the substrate are caused to apart away from the semiconductor element, which results in an increase in a length of each bonding-wire.
If such a highly densified semiconductor element is mounted on the low-cost substrate, the bonding-wires are not parallel to each other but gradually spread. Especially, in a case in which high-speed signal lines are constituted by differential pairs, a length of bonding-wires is increased, which may result in a case where an appropriate impedance, for example, 100 Ω, cannot be provided.
Additionally, since the bonding-wires are elongated, there is a problem that it is difficult to take impedance-matching of bonding-wires with wiring formed in the low-cost substrate. Although impedance-matching can also be achieved within the substrate by forming wiring in the substrate with a fine structure, it is not preferable to form a fine structure only in a part of the low-cost substrate.